Abstract

Galaxiella nigrostriata is a freshwater fish that is endemic to the seasonally dry coastal wetlands of south-west Western Australia and considered by the International Union for Conservation of Nature (IUCN) as lower risk–near threatened. This small fish (maximum total length <50 mm) aestivates in the sediment over the long, dry Mediterranean summer and its dispersal is limited by lack of habitat connectivity. The objective of this study was to identify the historical and contemporary genetic connectivity between populations of G. nigrostriata and to assess morphological variation between these populations. Results showed that all populations were genetically divergent and no mtDNA haplotypes were shared between populations. In contrast, morphological differentiation between individual populations was weak; however, pooling populations into two broad regions (Swan coastal plain and southern coast) resulted in clear morphological differentiation between these two groups. Based on these results, we postulate G. nigrostriata distribution last expanded in the early Pleistocene ~5.1 million years ago and have since been restricted to remnant wetlands in the immediate area. Galaxiella nigrostriata populations at the northern end of their range are small and are the most vulnerable to extinction. Conservation efforts are therefore required to ensure the survival of these genetically and morphologically distinctive Swan coastal plain populations.

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